speex

http://www.gnu.org/software/speex/
The Speex project aims to build a patent-free voice codec. Unlike codecs like MP3 and Ogg Vorbis, Speex is specially designed for compressing voice at low bit-rates (in the 8-32 kbps/channel range) for applications such as voice over IP (VoIP). Other possible applications include Internet audio streaming at low bit-rate, and archiving of speech data (e.g. voice mail). The Xiph.org license under which this software is released is similar to a revised BSD license.

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